Re: Case mapping of sharp s

[grischka <grishka@gmx.de>]

Kenichi Handa wrote:
> In article <4B0C32BF.2020708@gmx.de>, grischka <grishka@gmx.de> writes:
> 
>> DEC_BOTH is maybe not slower than INC_BOTH, but two DEC_BOTH
>> are (as with Andy's patch).  Moderately slower, still ;)
> 
> So, changing the current backward matching to forward
> matching should is effective.
> 

No, there is no such condition.  There are several ways to avoid
the duplicate DEC_POS, on being to handle the "pattern_len == 0"
case right at the top of the function, for all its branches.

>> The originally observed slowness was not because of the usage of
>> CHAR_TO_BYTE, but because of the flaws in CHAR_TO_BYTE, such as
>> using unrelated "best_below" and "best_above" in the same expression.
> 
>> For the numbers, with my 100MB file test case:
> 
>> backward search previously:
>> 	14 .. 90 s (random)
>> backward search with fixed CHAR_TO_BYTE:
>> 	5.6 s
> 
> I don't see any fix of CHAR_TO_BYTE in the current CVS
> code.  Where is it?

Those tests were made with ad hoc modifications as needed. There
was also some code to measure the times, of course.

>> In any case, with some tweaking it is possible to improve both
>> directions by ~70% (that is down to about 1 sec for the test
>> case).  I still don't know why boyer_moore with a one-char
>> pattern takes only 0.5 seconds though.  It's amazingly fast.
> 
> Are you comparing both methods with the same value of
> case-fold-search?

Same value, but not same search patterns.  One with "sharp s",
one without.

Actually I just wanted to check the facts with the originally in
this thread proposed "sharp s" patch, because some people wrote it
would be too slow.  FWIW I don't think it would be any problem.

>> Btw it seems that long loading time for the big file has much to
>> do with inefficient counting of newlines.  Appearently it takes
>> ~2 sec to load the file and then another ~6 sec to scan newlines.
>> It should be (far) under 0.5 sec.
> 
> Why is the code of counting newlines called when we just
> visit a file?

I have no idea why.  Opening the 100MB file would call scan_buffer
(for \n) 67637 times.  The file has 3142771 lines though, so I take
it back: it's probably not "counting newlines" in that sense.  Maybe
it comes from  "Loading cc-langs ..." which happens after the first
2 seconds.

--- grischka

> 
> ---
> Kenichi Handa
> handa@m17n.org
>